The present invention relates to a semiconductor device having cavities between metal interconnections and a method for fabricating the same.
With recent remarkable progress in semiconductor process technology, finer semiconductor elements and metal interconnections with higher integration have been pursued. With this trend toward finer size and higher integration, signal delay at metal interconnections has come to greatly influence the operation speed of semiconductor integrated circuinsorder to minimize signal delay at metal interconnections, proposed are methods for reducing the relative dielectric constant of an insulating film deposited between metal interconnections by forming cavities (ε=1.0) in the insulating film or by using an organic film as the insulating film, as described in Japanese Laid-Open Patent Publication No. 10-233448.
Conventional semiconductor devices adopting the above methods can reduce the relative dielectric constant to some extent. However, with further achievement of finer semiconductor elements and metal interconnections with higher integration, the distance between adjacent metal interconnections is further shortened. This increases the capacitance between metal interconnections and thus inevitably causes signal delay at metal interconnections.
To avoid the above trouble, the present inventors conceived a method for reducing the relative dielectric constant of an insulating film between metal interconnections, where an insulating film made of a fluorine-containing organic film is deposited between metal interconnections using a perfluorocarbon gas such as CF4 gas, C2F6 gas, C3F8 gas, and C4F8 gas and also cavities are formed in the insulating film.
However, the inventors noticed that the perfluorocarbon gases described above have a large global warming potential (GWP100) and thus have a possibility of causing global warming due to the greenhouse effect if used in high volume in an industrial scale.
In addition, the fluorine-containing organic film deposited using any of the above perfluorocarbon gases is poor in adhesion to an underlying film due to existence of a number of free fluorine atoms in the organic film.
Moreover, the fluorine-containing organic film deposited using any of the above perfluorocarbon gases lack denseness due to existence of a number of free fluorine atoms in the film, and thus poor in mechanical strength, heat resistance, and chemical resistance.